Let us first specify our model of concurrency. Words represent sequential behaviours: a
sequence of letters models a sequence of events, occurring on a single process. In a
concurrent setting involving multiple processes, we work with the well established
(Mazurkiewicz) traces [1]}, [2]}: a trace represents a
concurrent behaviour as a labelled partial order which captures the distribution of events
across processes, as well as causality and concurrency between them.
